The disclosure relates generally to wireless communications systems (WCSs), such as wireless distribution systems (WDSs), distributed antenna systems (DASs), remote radio head (RRH) systems, and small radio cell systems and, more particularly, to supporting self-interference cancellation in a WDS employing software-defined remote units.
Wireless customers are increasingly demanding wireless communications services, such as cellular communications services and Wireless Fidelity (WiFi) services. Thus, small cells, and, more recently, WiFi services, are being deployed indoors. At the same time, some wireless customers use their wireless communications devices in areas that are poorly serviced by conventional cellular networks, such as inside certain buildings or areas where there is little cellular coverage. One response to the intersection of these two concerns has been the use of WDSs. Examples of WDSs include DASs, RRH systems, and small radio cell systems (e.g., femtocell systems). WDSs include remote units configured to receive and transmit downlink communications signals to client devices within the antenna range of the respective remote units. WDSs can be particularly useful when deployed inside buildings or other indoor environments where the wireless communications devices may not otherwise be able to effectively receive radio frequency (RF) signals from a source.
In this regard, FIG. 1 illustrates a wireless distribution system (WDS) 100 that is configured to distribute communications services to remote coverage areas 102(1)(1)-102(M)(N), where ‘N’ is the number of remote coverage areas. The WDS 100 can be configured to support a variety of communications services that can include cellular communications services, wireless communications services, such as RF identification (RFID) tracking, WiFi, local area network (LAN), wireless LAN (WLAN), and wireless solutions (Bluetooth, WiFi Global Positioning System (GPS) signal-based, and others) for location-based services, and combinations thereof, as examples. For example, the WDS 100 may be a DAS or an RRH system. The remote coverage areas 102(1)(1)-102(M)(N) are created by and centered on remote units 104(1)(1)-104(M)(N) connected to a head-end unit (HEU) 106. The remote units 104(1)(1)-104(M)(N) are shown arranged in rows ‘1-M,’ each with columns ‘1-N’ for convenience, and are located in a building 108 or in an area of the building 108. The HEU 106 may be communicatively coupled to a base transceiver station (BTS) or a baseband unit (BBU). The HEU 106 receives downlink communications signals 112D from the BTS and/or the BBU to be communicated to the remote units 104(1)(1)-104(M)(N). The downlink communications signals 112D are communicated by the HEU 106 over a communications link 114 to the remote units 104(1)(1)-104(M)(N). The remote units 104(1)(1)-104(M)(N) are configured to receive the downlink communications signals 112D from the HEU 106 over the communications link 114. The remote units 104(1)(1)-104(M)(N) may include an RF transmitter/receiver (not shown) and a respective antenna operably connected to the RF transmitter/receiver to wirelessly distribute the communications services to user equipment (UE) 116 within the respective remote coverage areas 102(1)(1)-102(M)(N). The remote units 104(1)(1)-104(M)(N) are also configured to receive uplink communications signals 112U from the UE 116 in the respective remote coverage areas 102(1)(1)-102(M)(N) to be communicated to the HEU 106.
With continuing reference to FIG. 1, the WDS 100 is evolving from an Application Specific Integrated Circuit (ASIC)-based architecture into a software-defined-radio (SDR)-based structure. In a non-limiting example, the remote units 104(1)(1)-104(M)(N) may be provided as SDR-based remote units. The application of SDR improves flexibility of the remote units 104(1)(1)-104(M)(N) with respect to spectrum utilization, system configuration, and/or software upgrade. However, to support SDR, it is necessary to remove hardware-based narrow-band filters and/or duplexers from the remote units 104(1)(1)-104(M)(N). As a result, the remote units 104(1)(1)-104(M)(N) may not provide adequate suppression of in-band and out-of-band leakages, which are mainly induced by nonlinear components (e.g., power amplifier, filter, etc.) in the remote units 104(1)(1)-104(M)(N). These leakages cause or increase downlink-to-uplink (DL-to-UL) interference when the WDS 100 employs frequency-division duplex (FDD) and/or full-duplex (FDx) schemes and, consequently, reduce sensitivity and dynamic range of UL receivers for receiving the uplink communications signals 112U. As a result, both analog and digital self-interference cancellation (SIC) approaches have been developed to help mitigate the DL-to-UL interference in the WDS 100.
No admission is made that any reference cited herein constitutes prior art. Applicant expressly reserves the right to challenge the accuracy and pertinency of any cited documents.